1. Field of the Invention
The present invention relates to a method for manufacturing a photoelectric conversion element. More particularly, the invention relates to a method for manufacturing a photoelectric conversion element with high energy conversion efficiency but with less degradation with time. Especially, the present invention is suitably applicable to a photoelectric conversion element called a photovoltaic element or a photosensor.
2. Related Background Art
The following technology is known as a conventional method for manufacturing a photovoltaic element, which is one of the above-mentioned photoelectric conversion elements.
U.S. Pat. No. 4,400,409 discloses a continuous plasma CVD system employing the roll-to-roll method. It is understood that this apparatus can continuously manufacture a photovoltaic element having a pin junction by providing a plurality of glow discharge regions and continuously conveying a flexible substrate, having desired width and sufficient length, in the longitudinal direction thereof while depositing a necessary electroconductive semiconductor layer on the substrate in each of the glow discharge regions. In the same apparatus, gas gates are used in order to prevent dopant gas used for manufacturing each semiconductor layer from diffusing and mixing into other glow discharge regions. Specifically, the glow discharge regions are separated from one another by a slit-shaped separation passage and the system further employs means for keeping the separation passages under a flow of scavenging gas, for example, such as Ar or H.sub.2.
There are, however, the following problems in the method for forming the films by the above roll-to-roll method and apparatus.
(1) Even if mixing of gasous-state dopants were able to be substantially prevented by separating the formation spaces of the p-type semiconductor layer and the n-type semiconductor layer from the forming space of the i-type semiconductor layer, phosphorus (P) dopant in the n-type semiconductor layer would thermally diffuse into the i-type semiconductor layer, for example, during or after formation of the i-type semiconductor layer on the n-type semiconductor layer, which would weaken the n-i semiconductor junction, thus degrading the open-circuit voltage and fill factor of the photovoltaic element, and consequently, lowering the initial photoelectric conversion efficiency.
(2) Even if the photoelectric conversion efficiency immediately after manufacture was high, the dopant in the p-type semiconductor layer or in the n-type semiconductor layer would gradually thermally diffuse into the i-type semiconductor layer during practical use under various weather and location conditions, thus lowering reliability and promoting degradation of the photovoltaic element.